Well, I checked cables and dish, nothing changed.
One thing I should have mentioned before is that I have an in-line
amplifier that should give a gain of 20 dB, but MythTV always reports
4.8 dB despite the amplifier is present or not. In the latter case,
MythTV reports a signal strength less than 10%.
If MythTV is not fooling me, the amplifier is gone: 4.8 dB is less than
the gain it should give!
On the other hand, the signal strength is dramatically affected by the
amplifier.
I really can't figure this out.
Many thanks anyway to everybody for your kind help.
On Thu, 2009-06-04 at 18:18 -0400, William wrote:
> On 06/04/2009 05:59 PM, Robert McNamara wrote:
> >
> >
> > On Thu, Jun 4, 2009 at 2:53 PM, Andrea Giuliano
> > <sarkiaponius at alice.it> wrote:
> >
> > Robert McNamara wrote:
> >
> >
> > On Thu, Jun 4, 2009 at 1:51 PM, Andrea Giuliano
> > <sarkiaponius at alice.it> > <mailto:sarkiaponius at alice.it>> wrote:
> >
> > I'm seeing horrible artifacts in my DVB-S
> > recordings, even though
> > MythTV says the signal strength is 99%
> >
> >
> > Signal strength isn't what you think it is. Signal
> > strength is the strength of the electrical signal
> > between the card and the LNB, *not* an indication of
> > quality of the signal. More helpful for this is SNR
> > (Signal to Noise Ratio) and Bit Error. Low SNR or
> > high bit error means bad quality signal. Repoint
> > the dish.
> >
> >
> >
> >
> > Dear Robert,
> >
> > thanks for your kind answer. Can you please give me
> > reference values for SNR and Bit Error? I got 4.8 dB and
> > 2000-3000 for them, depending on the channels. Actually, SNR
> > seems to be constant, I mean it's alway 4.8 dB, while BE
> > changes instead.
> >
> > Also, my dish works perfectly fine with my stand alone
> > decoder (I have two cables from one dish), so I guess it's
> > not its fault.
> >
> > Best regards.
> >
> >
> > (Fixed top posting)
> >
> >
> > Hi Andrea,
> >
> >
> > Ideally, the BER should be 0 or extremely close to 0. Different
> > tuner devices have different signal sensitivities and different
> > decoders are more or less sensitive to errors in the stream. Both
> > are likely problems for you. You will almost definitely need to
> > point your dish more accurately. You can also check all your cable
> > termination, the cables themselves, and any power inserters for the
> > LNB.
> >
> >
> > Robert
> >
>> The issue is your 4.8 dB SNR. This is very weak and means your signal
> is very noisy. A good reading will be 10dB or more. You should be
> seeing a low BER starting at around 6dB however bad weather will cause
> you to have signal drop outs. You need to check antenna pointing, all
> the cables (water getting into the cable will ruin it even if it looks
> great so if you have any outside cable connections that are not
> waterproofed (covered with a boot or wrapped/painted with coax
> sealant) I would redo those connections and check signal strength
> again.
>> W.
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